Implement proper exception type hierarchy.

Each built-in exception is now a type, with base type BaseException.
C exceptions are created by passing a pointer to the exception type to
make an instance of.  When raising an exception from the VM, an
instance is created automatically if an exception type is raised (as
opposed to an exception instance).

Exception matching (RT_BINARY_OP_EXCEPTION_MATCH) is now proper.

Handling of parse error changed to match new exceptions.

mp_const_type renamed to mp_type_type for consistency.

py/objmodule.c

@@ -38,7 +38,7 @@ STATIC bool module_store_attr(mp_obj_t self_in, qstr attr, mp_obj_t value) {
 }
 
 const mp_obj_type_t module_type = {
-    { &mp_const_type },
+    { &mp_type_type },
     .name = MP_QSTR_module,
     .print = module_print,
     .load_attr = module_load_attr,